//The MIT License

//Copyright (c) 2009 Lluis Sanchez, Nick Darnell

//Permission is hereby granted, free of charge, to any person obtaining a copy
//of this software and associated documentation files (the "Software"), to deal
//in the Software without restriction, including without limitation the rights
//to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//copies of the Software, and to permit persons to whom the Software is
//furnished to do so, subject to the following conditions:

//The above copyright notice and this permission notice shall be included in
//all copies or substantial portions of the Software.

//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using System.Text;

using Polymorph.Properties;

namespace Polymorph
{
    /// <summary>
    /// The <see cref="CodeNullCoalesce"/> class represents the '??' operator.  It
    /// can be used return the non-null argument if there is one.
    /// </summary>
    /// <remarks>
    /// http://msdn.microsoft.com/en-us/library/ms173224.aspx
    /// </remarks>
    public class CodeNullCoalesce : CodeExpression
    {
        private CodeExpression m_exp1;
        private CodeExpression m_exp2;

        public CodeNullCoalesce(CodeExpression exp1, CodeExpression exp2)
        {
            m_exp1 = exp1;
            m_exp2 = exp2;

            if (m_exp1.ResultType.IsValueType || m_exp2.ResultType.IsValueType)
                throw new InvalidOperationException(Resources.NoValueTypesWithNullCoalesce);
        }

        public override void Generate(ILGenerator gen)
        {
            Label trueLabel = gen.DefineLabel();

            m_exp1.Generate(gen);
            gen.Emit(OpCodes.Dup);
            gen.Emit(OpCodes.Brtrue, trueLabel);
            gen.Emit(OpCodes.Pop);
            m_exp2.Generate(gen);
            gen.MarkLabel(trueLabel);
        }

        public override void PrintCode(CodeWriter cp)
        {
            m_exp1.PrintCode(cp);
            cp.Write(" ?? ");
            m_exp2.PrintCode(cp);
        }

        public override Type ResultType
        {
            get { return typeof(object); }
        }
    }
}